I am making uart communication using serial library. I can send and receive data, but when the number of bytes sent reaches 32768 or more, I get the error;

ValueError: byte must be in range(0,256)

function definition:

def Write_to_serial_port(value):
    ser.write([value])

function usage:

#...
    for i in data_buf[0:total_len]:  # data_buf is a list
        Write_to_serial_port(i)  
#...

The error message that occurs when the number of bytes sent reaches 32768:

An alternative serial port write function I tested:

def Write_to_serial_port(value):
    data = struct.pack('>B', value)
    ser.write(data)

Again the error message that occurs when the number of bytes sent reaches 32768:

I also tried periodically flushing the input and output buffers, but it didn't help. Any ideas on the solution?

EDIT1: The purpose of the program is to send the bytes in the binary file. While doing this, I send 128 bytes (from the binary file) and 13 bytes of CRC, file size etc information over the serial port in each cycle. data_buff size is 255 bytes but I am using 141 bytes.

function usage(Extended):

# ...
# Some definitions and assignments
# ...

while(bytes_remaining):
    if(bytes_remaining >= 128):
        len_to_read = 128
    else:
        len_to_read = bytes_remaining

    for x in range(len_to_read):
        file_read_value = bin_file.read(1)
        data_buf[9+x] = int(file_read_value[0])

    data_buf[0] = mem_write_cmd_total_len-1
    data_buf[1] = write_cmd
    data_buf[2] = word_to_byte(base_mem_address,1,1)
    data_buf[3] = word_to_byte(base_mem_address,2,1)
    data_buf[4] = word_to_byte(base_mem_address,3,1)
    data_buf[5] = word_to_byte(base_mem_address,4,1)
    data_buf[6] = gl_bin_file_sector_needed
    data_buf[7] = len_to_read
    data_buf[8] = send_count
    send_count = send_count + 1

    crc32       = get_crc(data_buf,mem_write_cmd_total_len - 4)
    data_buf[9 +len_to_read] = word_to_byte(crc32,1,1)
    data_buf[10+len_to_read] = word_to_byte(crc32,2,1)
    data_buf[11+len_to_read] = word_to_byte(crc32,3,1)
    data_buf[12+len_to_read] = word_to_byte(crc32,4,1)

    for i in data_buf[0:mem_write_cmd_total_len]:
            Write_to_serial_port(i)

#...

Error Message

EDIT2: I also tried splitting the 40KB binary file into 128byte chunk files and sending it. But I got the same error on the 256th file. I guess 256*128 = 32768 can't be a coincidence.